Device for chromium plating

ABSTRACT

Chromium plating apparatus comprising a main tank carrying the electrodes and an auxiliary tank adjacent the main tank and having fluid connections therewith. The electrolyte is adapted to be circulated between tanks with filtering, pumping and temperature control being effected in the auxiliary tank while plating is effected in the main tank. The main tank has platinum plated anode means which substantially decrease sludge formation during plating.

United States Patent 1 Takaysu 1 DEVICE FOR CHROMIUM PLATING [76] Inventor: Kiyosumi Takaysu, No. 2, 5-Chome,

l-lorita-Dori, Mizuho-ku, Nagoya, Japan [22] Filed: Jan. 29, 1973 21 Appl. No.: 327,483

[30] Foreign Application Priority Data Jan. 31, 1972 Japan 47-11266 [52] US. Cl 204/238, 204/239, 204/273, 204/274, 204/276, 204/290 F [51] Int. Cl B0lk 3/00, C22d 1/02 [58] Field of Search 204/237-241, 204/274276, 234-236, 273, 290 F [56] References Cited UNITED STATES PATENTS 2,710,832 Hart 204/238 X 1 Oct. 1, 1974 Otto 204/276 Morawetz et al. 204/276 X Primary ExaminerJohn H. Mack Assistant Examiner-D. R. Valentine Attorney, Agent, or FirmSilverman & Cass [57] ABSTRACT Chromium plating apparatus comprising a main tank carrying the electrodes and an auxiliary tank adjacent the main tank and having fluid connections therewith. The electrolyte is adapted to be circulated between tanks with filtering, pumping and temperature control being effected in the auxiliary tank while plating is effected in the main tank. The main tank has platinum plated anode means which substantially decrease sludge formation during plating.

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DEVICE FOR CHROMIUM PLATING BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a device for chromium plating, and more particularly to a chromium plating device including an independent auxiliary tank disposed adjacent to a main electrolyte tank for circulating the electrolyte through the two tanks while filtering and temperature controlling the electrolyte.

2. Description of the Prior Art Anodes in currently used chromium plating process are made of lead. The lead anodes are easily consumed in the course of plating, so that the consumed lead precipitates at the bottom of an electrolyte tank sludge, which tends to deteriorate the efficiency of the plating process. There has been no means available for removing the sludge while carrying out the plating. With the conventional process, the plating electrolyte is discarded after using it for a given time period together with sludge thus formed.

To discard the lead-containing electrolyte as a waste may cause an environmental pollution problem. Due to the precipitation of the sludge in the electrolyte, it has been necessary to use a large electrolyte tank, which requires an additional heating and cooling capacity. Thus. the overall efficiency of the conventional chromium plating process has been rather low.

It has been practised to apply a nickel or copper coating on a work before chromium plating the work. In order to achieve satisfactory chromium plating on such coating, the thickness of the coating has to be carefully controlled. Furthermore, the application of such coating of nickel or copper requires extra facilities and processing time. so that the overall plating process becomes costly.

Therefore, an object of the present invention is to mitigate the aforesaid difficulties of the conventional chromium plating process. by providing an improved device therefor,

SUMMARY OF'THE INVENTION According to the present invention, there is provided a chromium plating device which includes a main electrolyte tank having one or more platinum plated anode and an independent auxiliary tank disposed adjacent thereto. The auxiliary tank includes a filter and a temperature controlling means. such as a heat exchanger or a heater. together with a pump means for circulating the electrolyte through the main electrolyte tank and the auxiliary tank. While performing the chromium plating. the electrolyte is continuously circulated through the side tank. for filtering the electrolyte and controlling the temperature thereof.

The inventor has found out that. by continuously cleaning the electrolyte and controlling the temperature thereof, the quality of the chromium plating is greatly improved. One of the reasons for the improvement is the fact that the independent auxiliary tank with the filter installed therein facilitates the elimination of the sludge formation in the electrolyte tank. The auxiliary tank according to the present invention also reduces the overall tank volume. namely, the main electrolyte tank volume plus the independent auxiliary volume, as compared with that of conventional processes. The use of the platinum plated anode provides BRIEF DESCRIPTION OF THE DRAWING For a better understanding of the invention, reference is made to the accompanying drawing, in which:

FIG. 1 is a schematic plan view of a chromium plating device according to the present invention;

FIG. 2 is a partially cut away side view of the device of FIG. 1

FIGS. 3, 4, and 5 are diagrammatic illustrations of a pump, a filter, and an anode to be used in the device of FIG. 1;

FIG. 6 is a plan view of a different embodiment of the present invention; and

FIG. 7 is a side view of the embodiment of FIG. 6.

Like parts are designated by like numerals and symbols throughout the different figures of the drawing.

DESCRIPTION OF THE PREFERRED EMBODIMENT In the embodiment of FIGS. 1 and 2, a main electrolyte tank 1 carries chromium plating electrolyte, which can be any conventional electrolyte for such purpose. A typical example of the electrolyte contains 250 g/liter of chromic anhydride (CrO 2-3 g/liter of sulfuric acid (H 50 and 1-5 g/liter of three valued chromium (Cr An auxiliary tank 2 is disposed next to the main electrolyte tank 1, and a pump 2a is immersed in the auxiliary tank 2, so as to suck the electrolyte through a filter 4 and a connector conduit 6. In the embodiment of FIGS. 1 and 2, the pump 2a is separated from the electrolyte by a cylindrical wall, as shown in FIG. 3. The auxiliary tank 2 also includes a temperature control means 3, which is a steam actuated heat exchanger in the illustrated embodiment. A steam tube 8 delivers steam to the heat exchanger 3, while the drain therefrom is discharged to a drain tube 9. A separate immersion type electric heater 3a may be used along with the heat exchanger 3, as shown in FIG. 1. The levels of the electrolyte in the two tanks 1 and 2 are kept the same by a siphon pipe 6 with a vent valve 12. The discharge from the pump 2a is delivered to the bottom of the electrolyte tank 1 by a conduit 7.

Referring to FIGS. 1 and 2, a plurality of anode plates 13 are suspended from anode buses 16, while works 14 to be plated are hung from a cathode bus 15 so as to act as counterelectrodes. Two anode buses and one cathode bus are shown in the figure, which are connected to a DC. power source 19. The present invention, however, is not restricted to such number of buses. A control panel 17 is mounted on the auxiliary tank 2, and a power cable 18 is connected to an AC. or DC power source 20 for receiving electric power for energizing the heater 3a. A thermometer 11 is disposed in the electrolyte of the tank 1, which thermometer is connected to the control panel 17 through a control cable 10. The electric heater 3a may be automatically controlled on the basis of temperature signals from the thermometer 11. A means for such temperature responsive automatic control is known, so that no details of such means will be described here.

Referring to FIG. 5, the anode plate 13 to be used in the device according to the present invention comprises a corrugated metal plate, for instance, niobium or titanium plate, and one or both surfaces of the metal plate are plated with platinum. It is an important finding of the inventor that such platinum plated anode is effective in eliminating the formation of sludge. as experienced with conventional lead anode.

In operation. when the siphon pipe 6 is evacuated through the vent valve 12 and sealed therby. the electrolytes in the two tanks 1 and 2 are communicated with each other. As the pump 2a delivers the electrolyte from the side tank 2 to the electrolyte tank 1, the siphon pipe returns the corresponding amount of the electrolyte from the main electrolyte tank I to the auxiliary tank 2. The temperature control means, such the heat exchanger 3 and the immersion type heater 3a, keeps the electrolyte at an optimal temperature for the plating, for instance, at about 50 to 55C. While the electrolyte circulates through the two tanks. the filter 4 removes any undesirable components therein. for instance, sludge is eliminated by the filter 4. Whereby, the electrolyte in the plating electrolyte tank 1 is kept clean and clear at the optimal temperature.

Chromium film formed by conventional chromium plating process inevitably involves pin holes therein. The inventors has found out that. by keeping the electrolyte clean and controlling the electrolyte temperature at an optimal level, the formation of the pin holes can be suppressed.

In the illustrated embodiment, the heat exchanger 3 is shown as a steam heater. The heat exchanger can be a cooler. in which a suitable coolant is passed therethrough. when the ambient temperature and other op-. erating conditions require the cooling of the electrolyte.

FIGS. 6 and 7 illustrate a second embodiment of the present invention. In this embodiment, an auxiliary tank 2 having a partition wall la is used. so as to house a filter 4 in one of the two chambers thus partitioned, while a heat exchanger 3 and an immersible pump are disposed in the other chamber. Major differences of this second embodiment from the aforesaid first embodiment of FIGS. 1 to 5 are as follows.

a. In the first embodiment of FIGS. 1 to 5, the filter l is on the intake side of the pump 2a. On the other hand, with the second embodiment of FIGS. 6 and 7, the filter 4 is on the discharge side of the pump 2a.

b. The first embodiment of FIGS. 1 to 5 is primarily directed to automatic temperature control with the im mersion type heater 3a. but the second embodiment is not.

In either of the two embodiments, the filtered electrolyte is delivered to the bottom of the main electrolyte tank 1. so that an upwardly directed electrolyte flow is forcibly generated in the main electrolyte tank I. This upwardly directed electrolyte causes agitation, especially in the proximity of the works 14, so that uni form chromium film can be plated thereon. Whereby, the quality of the chromium plating can be greatly improved. If necessary. air bubbles may be delivered together with the filtered electrolyte, for improving the agitation.

The salient features of the present invention can be summarized as follows.

1. Temperature control, i.e., heating and cooling. and filtering of electrolyte can be carried out in an independent auxiliary tank. so that the main electrolyte tank can be made smaller than a conventional main electrolyte tank. and the overall volume of the electrolyte can be reduced. The filter thus mounted on the auxiliary tank can easily be cleansed for regeneration, as compared with the case in which a filter is mounted on the main electrolyte tank.

2. Auxiliary equipment and piping around the electrolyte tank are greatly simplified, so that the floor space for the chromium plating can be reduced. Furthermore. the temperature and cleanliness control of the electrolyte can be carried out easily.

3. The amount of electrolyte to be removed from the chromium plating device can be minimized. This means an economy of the electrolyte, for reducing the plating cost. Furthermore, it prevents environmental pollution.

4. As compared with a conventional electrolyte tank allowing sludge formation therein, the present invention makes it possible to reduce the tank depth by about 20 percent. because the sludge is eliminated as far as the main electrolyte tank 1 is concerned. Thus, the tank can be made smaller, and the amount of the electrolyte is reduced, so as to cut down the plating cost. Furthermore, the reduced amount of the electrolyte simplifies the control thereof.

5. Automatic chromium plating with automatic temperature control is possible. In this case. by properly coordinating the size of the auxiliary tank 2 with that of the main electrolyte tank 1, the overall size and the total amount of theelectrolyte can be minimized.

6. With reduction of the overallsize, the risk of leakage at the temperature control, filter. and other piping can be minimized.

7. The need of the complete renewal of the electrolyte can virtually be eliminated. On the other hand. with conventional devices. the sludge requires the complete renewal of the electrolyte. at least once in a few years. and such renewal means the disposal of the sludge, which might cause environmental pollution.

8. The cleanness of the electrolyte, as combined with the optimal temperature and the agitation, results in an excellent chromium plating.

9. The elimination of the sludge from the main plating electrolyte tank improves the agitation and even temperature distribution in the electrolyte tank, so that the efficiency of the temperature control can be materially improved.

l0. Thin and pin-hole-free chromium film can be plated. More particularly. a chromium film of medium thickness between a conventional hard chromium film (i.e., a thick pure chromium film) and a conventional double layer chromium film (i.e.. chromium film on copper or nickel coating) can be achieved at a low cost.

What is claimed is:

l. A device for chromium plating. comprising, a main tank for carrying electrolyte containing chromium ions; at least one anode adapted to be disposed in the electrolyte of the main tank and comprising at least one platinum plated corrugated plate made of a metal selected from the group consisting of niobium and titanium; cathode bus means adapted to be disposed above the electrolyte and arranged to carry workpieces to be chromium plated and further adapted to provide for immersing the said workpieces in said electrolyte when the said main tank is properly filled with electrolyte whereby to enable such workpieces to serve as counterelcctrode means; an auxiliary tank disposed adjacent the main tank; a siphon connected between tanks and adapted to transfer electrolyte from said main tank to said auxiliary tank; heat exchanger means disposed in the auxiliary tank for heating and cooling electrolyte which may be carried therein; a filter disposed in said auxiliary tank; pump means disposed in said auxiliary tank and arranged for forcibly recirculating the electrolyte through the tanks through said filter and having intake and discharge sides; and pipe means extending from said discharge side of said pump means to the bottom of said main tank at a location below said cathode bus means, said pipe means having passageways therein arranged to direct the electrolyte from the pump means toward said cathode bus means, whereby in operation the electrolyte discharge from said pump means acts to agitate the electrolyte in the proximity of workpieces suspended from the cathode bus means.

2. A device according to claim 1, wherein said heat exchanger means includes an immersion type electric I heater.

3. A device according to claim 2 and further comprising a thermometer disposed in the electrolyte of said main tank, a control panel mounted on said auxiliary tank and having electric switching means, and a control cable connecting said switching means to said thermometer and to said electric heater, whereby said electric heater is so controlled as to keep the electrolyte at a predetermined temperature.

4. A device according to claim 1, wherein said auxiliary tank has a partition wall defining two chambers therein, and said filter being housed in one of the two chambers.

5. A device according to claim 1, wherein said filter is disposed at the intake side of said pump means.

6. A device according to claim 1, wherein said filter is disposed at the discharge side of the pump means. 

1. A device for chromium plating, comprising, a main tank for carrying electrolyte containing chromium ions; at least one anode adapted to be disposed in the electrolyte of the main tank and comprising at least one platinum plated corrugated plate made of a metal selected from the group consisting of niobium and titanium; cathode bus means adapted to be disposed above the electrolyte and arranged to carry workpieces to be chromium plated and further adapted to provide for immersing the said workpieces in said electrolyte when the said main tank is properly filled with electrolyte whereby to enable such workpieces to serve as counterelectrode means; an auxiliary tank disposed adjacent the main tank; a siphon connected between tanks and adapted to transfer electrolyte from said main tank to said auxiliary tank; heat exchanger means disposed in the auxiliary tank for heating and cooling electrolyte which may be carried therein; a filter disposed in said auxiliary tank; pump means disposed in said auxiliary tank and arranged for forcibly recirculating the electrolyte through the tanks through said filter and having intake and discharge sides; and pipe means extending from said discharge side of said pump means to the bottom of said main tank at a location below said cathode bus means, said pipe means having passageways therein arranged to direct the electrolyte from the pump means toward said cathode bus means, whereby in operation the electrolyte discharge from said pump means acts to agitate the electrolyte in the proximity of workpieces suspended from the cathode bus means.
 2. A device according to claim 1, wherein said heat exchanger means includes an immersion type electric heater.
 3. A device according to claim 2 and further comprising a thermometer disposed in the electrolyte of said main tank, a control panel mounted on said auxiliary tank and having electric switching means, and a control cable connecting said switching means to said thermometer and to said electric heater, whereby said electric heater is so controlled as to keep the electrolyte at a predetermined temperature.
 4. A device according to claim 1, wherein said auxiliary tank has a partition wall defining two chambers therein, and said filter being housed in one of the two chambers.
 5. A device according to claim 1, wherein said filter is disposed at the intake side of said pump means.
 6. A device according to claim 1, wHerein said filter is disposed at the discharge side of the pump means. 